Which type of deposit has a higher percentage of gem-quality diamonds?

• A. Primary Deposits
• B. Alluvial deposits
• C. Secondary Deposits
• D. No gem-quality diamonds in either

Answer: (C)

Diamonds that have moved from their original source and settled in new settings are more effectively concentrated in secondary deposits. When diamonds are eroded out of their primary host rock and carried by water, the natural sorting by gravity and flow tends to pile up heavier, well-formed stones in certain pockets, while many poorer-quality or smaller stones are dispersed or damaged. This leads to a higher proportion of gem-quality stones in secondary (placer) deposits compared with the original rock where a broad mix of qualities remains trapped. So, the general pattern is that secondary deposits yield a greater share of gem-quality diamonds. Primary deposits can contain good stones too, but the overall quality mix is broader and often includes more industrial-grade material.